1. Field of the Invention
The present invention is related to a multi-function testing device and its testing method, and more particularly, to a measuring device with the function of automatically determining the type of device under test (DUT) without selection of switch and its testing method, for example, a multi-meter with function of automatically determining the type of DUT.
2. Description of the Prior Art
At present every automatic function selecting multi-meter is able to display digital measured values, for example, displaying direct current voltage value or alternating current voltage value, resistor value or capacitor value, diode or circuit passageway test result, etc. The above-mentioned functions are generally switched by rotating rotation knob or pressing button, and the user has to determine and select measuring function by himself and manually switch to measuring function that is selected to perform.
Although some multi-meters are claimed to be having intelligent automatic testing function, yet the so-called intelligent automatic testing function is actualized by manually adjusting the function selecting switch of multi-meter to function for measuring a DUT. For example, when the DUT is a resistor, then before the measurement, the function selecting switch of multi-meter needs to be adjusted (or switched) to the function for measuring resistor; the probe at input end is then used to measure the resistor under test, whereas the multi-meter with intelligent automatic testing function selects appropriate resistor measuring range for measuring and it is not necessary for the user to perform tests step by step from the highest resistor value (100 M ohms for example) to find the appropriate resistor value. For another example, when the DUT is under open/short detection, the function selecting switch needs to be switched to the function for open/short detection, and the multi-meter automatically performs test and displays whether the DUT is open or short.
In addition, since multi-meter is equipped with multiple functions, thus for a user not very familiar with electrical properties, it is not enough only to have a multi-meter with above-mentioned function of automatically selecting measuring range. As in the process of measuring, the user may not be able to switch to the right measuring function to be performed, which then leads to errors in measuring. For example, when a DUT is an alternating current voltage source, if the user switches to the function for measuring direct current voltage and the measurement of this signal source is performed and results in a near-zero value as measured value, then not only is the measured result erroneous, but the user is also misled to consider that the DUT is with no voltage and thus neglects the risk of electrical burns. For another example, among circuit elements, diode and resistor often have similar appearances and it is often not easy to differentiate one from another for a beginner; if a user mistakes diode to be resistor and performs measurement, a reasonable value can still be obtained, which results in misusage of electric elements without the user being aware of it.
At present there are multi-meters further equipped with function of automatically selecting DUT which helps the user select the right type of DUT, as disclosed in U.S. Pat. Nos. 5,142,221, 5,557,197, and 6,646,562. However, the automatic selecting functions as disclosed in above-mentioned patents cannot cover all of the following functions commonly used: direct current voltage/alternating current voltage/direct current/alternating current/resistor/capacitor/diode/short detection. The present invention thus provides a fast detecting process which is able to detect the type of DUT in a short time and performs measurement and detecting range of which covers all functions of above-mentioned multi-meters. The convenience of operation and the accuracy of measurement can thus be greatly enhanced.
Current multi-meters can already be operated in a simple way. However, when testing is to be actually performed on a complex circuit, there is still need to first determine what type the DUT is and then manually switch the function selecting switch of multi-meter to the appropriate function for the automatic testing function of multi-meter to operate and to obtain the measured result. In addition, when a high voltage signal is inputted, if the measuring function is wrongly selected, not only will the circuit in the measuring device be damaged, but the operator of measuring device may also be harmed. Process of such kind not only decreases the efficiency of work and causes inconvenience, but also leads to longer time in doubt and possible damages to both the measuring device and the operator, particularly when the selection of measuring function is erroneous.
It is thus clear that there is still room for improvement considering the convenience of operating multi-meter of prior art.